The invention starts from a three-phase extraction tower having two chambers which are connected in their top and bottom parts by connection channels and have ports for feeding and removing the first and second disperse phase.
A multiple phase extractor of this type can be used in chemical, hydrometallurgical, microbiological and other industrial branches for the separation, extraction, concentration and purification of substances.
Apparatuses for carrying out processes of the three-phase liquid extraction are known in the form of a two-chamber system, the two chambers being connected together in the upper part or having a porous dividing wall. The chambers are filled with a continuous phase through which two disperse phases, which are not soluble in the continuous phase, are passed in the form of droplets. In this case, substances are transferred from a disperse phase (raffinate phase) through the continuous phase (also termed liquid-membrane phase) into the other disperse phase (extract phase). (See, for example, Journal xe2x80x9cTheoretische Grundlagen der chemischen Technologiexe2x80x9d 1984, Part 18; No. 6, pp. 736-738)
These apparatuses require improvement with respect to their performance and extension to multistage processes.
From the technical standpoint and from the effect achievable, the three-phase extraction tower which consists of a first and second chamber filled with the continuous phase (liquid membrane) approximates most closely to the proposed apparatuses. The chambers have apparatuses for dispersing the respective phase and are connected to one another by overflows for circulating the continuous phase. The overflows are constructed in the form of tubes which connect the upper and bottom part of each of the chambers to one another. The extractor is equipped with ports for feeding and removing the first and second disperse phase. (Russian patent application no. 94-015776/26 (015406) of 27.04.94).
The phase to be dispersed, which is the starting solution (raffinate), and the solvent (extract phase) are each divided by a dispersion apparatus in the appropriate chamber into droplets which move as a droplet stream through the continuous phase. Because of the difference in density between the dispersions in the first and second chambers, the continuous phase circulates through the upper and lower overflows, so that the substances to be extracted transfer from one chamber into the other and from the first phase to be dispersed into the second.
The disadvantage of the known three-phase extraction tower is the high degree of axial mixing in the chambers, in particular in the chamber having countercurrent flow of the contacting phases, which, in the sense of countercurrent flow extraction, means a decrease in the efficiency.
The object of the invention is to increase the efficacy of the three-phase extraction tower.
This object is achieved according to the invention starting from the apparatus described at the outset by means of the fact that at least one chamber is equipped with internals.
According to a preferred embodiment, the internals are designed as packings.
Alternatively, the internals can also be designed as perforated plates.
Advantageously, the internals are constructed in the form of stirrer elements.
Preferably, the chambers have end separators which are connected by overflows.
A further development of the invention is characterized in that below a first stage having two chambers, further series-connected stages of the same construction are arranged.
Equipping the chambers with internals which are designed as packings (arranged or dumped) or perforated plates decreases the axial mixing of the circulating stream of the continuous phase, so that its flow behaviour is approximately comparable to plug-flow circulation. This considerably increases the efficicacy of all of the mass transport between the two chambers and between the first and second disperse phase. The installation of stirrer or mixing elements (conventional stirrers, reciprocating plates etc.) in one or both chambers also contributes to this. In this case, the exchange area is also increased and the axial mixing of the respective disperse phase is decreased.
Equipping the chambers with end separators which are connected by connection channels or overflows decreases the mixing of the two disperse phases.
The series connection of a plurality of stages in two-chamber towers can markedly improve the efficiency of the extraction process.